The present invention relates to apparatus for selective engagement with an advancing web. In particular, the invention relates most specifically to apparatus and methods for the assembly and ready replacement of covers for rolls used to engage advancing webs.
It is well known to provide a cylindrical roll with specifically desired frictional characteristics on its exterior surface for use in web advancement and treatment processes. In the textile industry, the use of rolls to convey, pull and hold back fabric is very common, and these rolls are referred to as pull rolls. For instance, weaving machines, inspection machines, finishing lines, napping lines, sueding lines and dye lines all contain numerous pull rolls to aid in performing such operations. Steel or aluminum rolls themselves do not provide surfaces with sufficient frictional forces to keep fabric from slipping in most applications. Such rolls are thus covered or coated with a material which aids in gently guiding the fabric through the textile processing machinery without distorting its weave, yet keeping the fabric relatively uniform in advancement and spread.
The cover on a pull roll may have a low or high coefficient of friction, depending upon the particular fabric, process characteristics and desired engagement or traverse of the pull roll with the fabric. Numerous materials have been used to define the frictional interaction between the roll surface and the fabric. Typical prior art pull roll cover materials include cork, rubber, modified cork, smooth rubber, sandpaper and bristle-bearing materials. During use of such materials, their frictional characteristics can change. For instance, cork and rubber-based materials tend to glaze over as they wear and become smoother, presenting a change in friction level to the fabric web over time. This can result in a slow deterioration of fabric quality or increased motor power usage due to slipping, which are both difficult to detect. In addition, abrasives such as sandpaper do not wear evenly, because of their random surface textures. Further, while abrasives such as sandpaper present higher frictional characteristics for a pull roll cover, they are non-uniform by design and thus are unsuitable for some fabric webs because their non-uniformity results in damage to the fabric. Pull roll covers based on a bristled structure (such as the BRUSHLON.RTM. brush material of Minnesota Mining and Manufacturing Company, St. Paul, Minn.), are also random in bristle dispersion and alignment.
A pull roll cover material is typically applied by helically wrapping a two to three inch wide strip of the material down the length of the roll. Adhesion of the material to the roll surface has been accomplished by the use of contact cements, spray adhesives, and nonrepositionable pressure sensitive adhesives. To remove such roll covers from a roll requires removal of the roll from the textile processing machinery, and in some instances the machining off of the covering. These types of adhesion arrangements typically lead to buildups of adhesive on the roll surface over time, contain flammable solvents in the adhesive, require long cure times on the roll surface, and in many cases require the use of flammable solvents for roll clean-up. Environmental concerns and restrictions now prohibit the use of many of these adhesives in textile plants, thereby requiring the removal and application of roll surfaces by outside parties and at locations other than the textile processing facility.
One type of pull roll cover forms a cylindrical brush, as disclosed in Dupre U.S. Pat. No. 4,627,127. In Dupre, a fabric strip containing bristles on an outer peripheral surface thereof is wrapped in a helix about a cylinder. The fabric strip is adhered to the cylinder by means of an adhesive such as polyurethane. Through use, the bristles wear down and the remaining covering must be replaced. To remove such a covering bonded to the cylinder by an adhesive requires the use of solvents. This can be messy, relatively time consuming (resulting in machine downtime) and, as mentioned above, the use of solvents to remove adhesives creates undesirable hazardous waste removal issues.
In an effort to address these environmental concerns, and also to form a more readily replaceable pull roll cover, mechanical fastening schemes (such as hook-and-loop fastener structures) have been used instead of adhesives to bond the cover material to the roll. One roll cover material currently available for this purpose has 1/8" trim nylon 6.12 bristle BRUSHLON.RTM. brush material (available from Minnesota Mining and Manufacturing Company, St. Paul, Minn.) on one side of a support substrate, with a loop structure material on its other side. A hook structure material (having projecting hooks or capped stems thereon) is bonded to the exterior surface of the cylindrical roll, typically in strip form wrapped thereabout in a helix. The bristle/loop structure assembly is also wrapped in strip form in a helix about the cylindrical roll, with the loop structure interengaging with the hook structure to affix the bristle/loop structure assembly to the pull roll cylinder. While this arrangement allows for ready removal of the exterior bristle bearing fabric, and replacement thereof with an alternative roll exterior material having a loop structure backing, it also is not ideal. The combination of the bristles, support substrate and hook-and-loop fastener form a pull roll cover assembly having a relatively high profile. Further, if the pull roll cover material is wrapped in an imperfect helix along the roll, one or more hooks may be inadvertently exposed from the hook structure material mounted on the cylindrical roll. These exposed hooks can damage the fabric web being traversed by the roll by picking or tearing at fabric fibers, creasing the fabric, scuffing its surface or by causing some other similar surface phenomenon.
A typical textile pull roll will have a diameter in the range of 4-12 inches, but can be smaller or larger. A high profile (relatively thick) pull roll cover increases the effective diameter of a pull roll, and this effect is even more significant on a smaller diameter pull roll (e.g., a 1-3 inch diameter pull roll). It is an undesirable necessity that drive roll speeds be adjusted if a significant change in roll diameter results from the application of a roll cover, and thus a pull roll cover should be as thin as possible.
The pickup or transfer of particulates or fluids by a pull roll cover is also undesirable. A cover material is also unacceptable if it allows lint and fiber build-up thereon during use. In addition, in some applications the roll or fabric web will be wet. For example, a roll cover must not pick up and hold fabric dyes from the manufacturing process. Color changes are common and the transfer of dyes from one fabric lot to another is unacceptable.
In view of the disadvantages associated with the various pull roll cover schemes of the prior art, it is desirable to provide a pull roll that has a changeable exterior covering, wherein the covering is relatively inexpensive, reusable or replaceable, easily and securely attachable to the cylindrical pull roll and which, in use, does not allow undesirable contact or damage to the web traversed thereby. A pull roll cover and its attachment means should also have as low a profile as possible, and the covers should be resistive to collecting lint or fibers, and resistive to the transfer of dyes between webs. In addition, an exterior material for a pull roll cover is desired that has a long life, and provides the desired frictional characteristics, or range of frictional characteristics for customer flexibility.